cap sensing UNLISTED

Not provided.

This circuit demonstrates capacitance sensing using two microcontroller pins, one resistor, and one reference capacitor. Using the the microcontroller's tri-state outputs, we use the unknown capacitance Ctouch to charge the reference capacitor C1 in a series of steps. Each cycle, check if the voltage at Pin A is enough to read "high" while Pin A is high-impedance and Pin B is held low. The number of cycles this takes is inversely proportional to the value of the unknown capacitance.

The top block generates a pair of 25% duty cycle square waves 180 degrees out of phase with each other. The two signals are used to toggle pin A between Z and 1, and pin B between Z and 0. The reset signal holds both pins low initially to ensure that C1 is discharged before the measurement cycle.

You would want to use a larger value for C1 in a real circuit to increase the number of steps needed, and thus the resolution. The low value is used here to show the concept quickly without requiring a long simulation.